Professional surfers have flocked to the Atlantic coastlines of France, Cornwall, Ireland and Portugal to ride waves up to 18 metres high caused by a low pressure system dubbed "the black swell".

South African big wave rider Grant "Twiggy" Baker was joined on Tuesday by Portuguese, French and American surfers at the Belharra break off the coast of south-west France, where they prepared to take on 15-metre (49ft) waves. The Met Office's Seven Stones buoy off the tip of Cornwall recorded 9-metre swells on Tuesday morning, while the waves piling into Mullaghmore Head in County Sligo, Ireland, reached 12 metres on Monday, according to some reports.

The surf forecasting company Magic Seaweed said the remarkable conditions were caused by an area of 15-metre waves in the north Atlantic the size of the Iberian peninsula, and the extent and ferocity of the winds passing over the ocean surface was causing the powerful swells.

"We've had bigger systems than this, but what we don't get is people wanting to ride them," said Ed Temperley, Magic Seaweed's editor. "Now we are seeing more desire to ride them and the wind is coming from the south which means that places like Mullaghmore Head are rideable."

He told the Guardian on Tuesday: "There were some hairy rides and there were a few where I went right down into the water.," Brittan said. "I can tell it was very dark down there yesterday. Down there was living repeatedly rabbit punched while diving in the deep."

Brittan said he and his fellow surfers rushed to the Sligo coast because the worst of the storms were further south, battering the shorelines of counties Clare and Galway.

The surfer – who has been a big wave rider for eight years – said the waves were "really huge, some of the biggest I've seen".

With the weather predicted to calm around Ireland over the next few days, Brittan said he was not too disappointed to be out of action for a while.

"To be honest I really need a rest after yesterday. We will keep our eyes on the forecast to see when the next big storms roll in and we will be out looking for the huge waves again," he said.

Owen Murphy, at the Bundoran Surf Company, near Mullaghmore, said 20 surfers went out into 6-metre to 12-metre swells on Monday, towed into the waves by a dozen jet ski riders, including Nick Von Rupp, Portugal's 2011 national champion. Andrew Cotton, one of the UK's leading big wave riders, who has ridden what is considered to be one of the biggest waves ever in Portugal, was among the riders of the reef break.

"The waves were 20 to 30ft high and 20ft wide and they break really heavily," he said. "You have to be a really good surfer. Often there is nowhere to go but inside the barrel.

"The biggest wave I've surfed in Portugal is bigger and there's a lot of water, but it is quite 'slopey'. The fear there is drowning; that you'll get pushed very deep. Here it is almost like a round pipe. It is big, shallow and dangerous. The biggest fear is you fall and get slammed into rock."

A jet-ski prepares to bring surfers out to sea at Mullaghmore, County Sligo, Ireland. Photograph: Brian Lawless/PA

The swell has sparked a surf safari among some riders who have been searching out spots that would otherwise be far too calm to surf.

Stuart Campbell, the Woolacombe-based 2011 British champion, surfed in "double overhead" conditions at a sheltered spot near Lynmouth and said other surfers had sought out breaks as far up the Bristol channel as near to Minehead, where surfing is rarely possible.

"There has been a big upside to this storm for surfers," he said. "A lot of guys have been exploring different spots. People are posting photos of waves [online] that have never been surfed before."